//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// SPDX-FileCopyrightText: Copyright (c) 2022 NVIDIA CORPORATION & AFFILIATES.
//
//===----------------------------------------------------------------------===//
#ifndef _CUDA_STD___EXPECTED_EXPECTED_H
#define _CUDA_STD___EXPECTED_EXPECTED_H

#include <cuda/std/detail/__config>

#if defined(_CCCL_IMPLICIT_SYSTEM_HEADER_GCC)
#  pragma GCC system_header
#elif defined(_CCCL_IMPLICIT_SYSTEM_HEADER_CLANG)
#  pragma clang system_header
#elif defined(_CCCL_IMPLICIT_SYSTEM_HEADER_MSVC)
#  pragma system_header
#endif // no system header

#include <cuda/std/__concepts/invocable.h>
#include <cuda/std/__expected/bad_expected_access.h>
#include <cuda/std/__expected/expected_base.h>
#include <cuda/std/__expected/unexpect.h>
#include <cuda/std/__expected/unexpected.h>
#include <cuda/std/__memory/addressof.h>
#include <cuda/std/__memory/construct_at.h>
#include <cuda/std/__type_traits/conjunction.h>
#include <cuda/std/__type_traits/disjunction.h>
#include <cuda/std/__type_traits/is_assignable.h>
#include <cuda/std/__type_traits/is_constructible.h>
#include <cuda/std/__type_traits/is_convertible.h>
#include <cuda/std/__type_traits/is_copy_assignable.h>
#include <cuda/std/__type_traits/is_copy_constructible.h>
#include <cuda/std/__type_traits/is_default_constructible.h>
#include <cuda/std/__type_traits/is_function.h>
#include <cuda/std/__type_traits/is_move_assignable.h>
#include <cuda/std/__type_traits/is_move_constructible.h>
#include <cuda/std/__type_traits/is_nothrow_constructible.h>
#include <cuda/std/__type_traits/is_nothrow_copy_assignable.h>
#include <cuda/std/__type_traits/is_nothrow_copy_constructible.h>
#include <cuda/std/__type_traits/is_nothrow_default_constructible.h>
#include <cuda/std/__type_traits/is_nothrow_move_assignable.h>
#include <cuda/std/__type_traits/is_nothrow_move_constructible.h>
#include <cuda/std/__type_traits/is_reference.h>
#include <cuda/std/__type_traits/is_same.h>
#include <cuda/std/__type_traits/is_swappable.h>
#include <cuda/std/__type_traits/is_trivially_copy_constructible.h>
#include <cuda/std/__type_traits/is_trivially_destructible.h>
#include <cuda/std/__type_traits/is_trivially_move_constructible.h>
#include <cuda/std/__type_traits/is_void.h>
#include <cuda/std/__type_traits/lazy.h>
#include <cuda/std/__type_traits/negation.h>
#include <cuda/std/__type_traits/remove_cv.h>
#include <cuda/std/__type_traits/remove_cvref.h>
#include <cuda/std/__utility/as_const.h>
#include <cuda/std/__utility/exception_guard.h>
#include <cuda/std/__utility/forward.h>
#include <cuda/std/__utility/in_place.h>
#include <cuda/std/__utility/move.h>
#include <cuda/std/__utility/swap.h>
#include <cuda/std/initializer_list>

#include <cuda/std/__cccl/prologue.h>

_CCCL_BEGIN_NAMESPACE_CUDA_STD

template <class _Tp, class _Err>
class expected;

namespace __expected
{
template <class _Tp, class _Err>
inline constexpr bool __valid_expected =
  !is_reference_v<_Tp> && !is_function_v<_Tp> && !is_same_v<remove_cv_t<_Tp>, in_place_t>
  && !is_same_v<remove_cv_t<_Tp>, unexpect_t> && !__unexpected::__is_unexpected<remove_cv_t<_Tp>>
  && __unexpected::__valid_unexpected<_Err>;

template <class _Tp>
inline constexpr bool __is_expected = false;

template <class _Tp, class _Err>
inline constexpr bool __is_expected<expected<_Tp, _Err>> = true;

template <class _Tp>
inline constexpr bool __is_expected_nonvoid = __is_expected<_Tp>;

template <class _Err>
inline constexpr bool __is_expected_nonvoid<expected<void, _Err>> = false;

template <class _Tp, class _Err>
inline constexpr bool __can_swap =
  is_swappable_v<_Tp> && is_swappable_v<_Err> && is_move_constructible_v<_Tp> && is_move_constructible_v<_Err>
  && (is_nothrow_move_constructible_v<_Tp> || is_nothrow_move_constructible_v<_Err>);

template <class _Err>
inline constexpr bool __can_swap<void, _Err> = is_swappable_v<_Err> && is_move_constructible_v<_Err>;
} // namespace __expected

template <class _Tp, class _Err>
class expected : private __expected_move_assign<_Tp, _Err>
{
  using __base = __expected_move_assign<_Tp, _Err>;

  static_assert(__expected::__valid_expected<_Tp, _Err>,
                "[expected.object.general] A program that instantiates the definition of template expected<T, E> for a "
                "reference type, a function type, or for possibly cv-qualified types in_place_t, unexpect_t, or a "
                "specialization of unexpected for the T parameter is ill-formed. A program that instantiates the "
                "definition of the template expected<T, E> with a type for the E parameter that is not a valid "
                "template argument for unexpected is ill-formed.");

  template <class, class>
  friend class expected;

public:
  using value_type      = _Tp;
  using error_type      = _Err;
  using unexpected_type = unexpected<_Err>;

  template <class _Up>
  using rebind = expected<_Up, error_type>;

  // [expected.object.ctor], constructors
  _CCCL_TEMPLATE(class _Tp2 = _Tp)
  _CCCL_REQUIRES(is_default_constructible_v<_Tp2>)
  _CCCL_API constexpr expected() noexcept(is_nothrow_default_constructible_v<_Tp2>)
      : __base(true)
  {}

  _CCCL_HIDE_FROM_ABI constexpr expected(const expected&)            = default;
  _CCCL_HIDE_FROM_ABI constexpr expected(expected&&)                 = default;
  _CCCL_HIDE_FROM_ABI constexpr expected& operator=(const expected&) = default;
  _CCCL_HIDE_FROM_ABI constexpr expected& operator=(expected&&)      = default;

private:
  template <class _Up, class _OtherErr, class _UfQual, class _OtherErrQual>
  static constexpr bool __can_convert =
    is_constructible_v<_Tp, _UfQual> && is_constructible_v<_Err, _OtherErrQual>
    && !is_constructible_v<_Tp, expected<_Up, _OtherErr>&> //
    && !is_constructible_v<_Tp, expected<_Up, _OtherErr>> //
    && !is_constructible_v<_Tp, const expected<_Up, _OtherErr>&>
    && !is_constructible_v<_Tp, const expected<_Up, _OtherErr>> //
    && !is_convertible_v<expected<_Up, _OtherErr>&, _Tp> //
    && !is_convertible_v<expected<_Up, _OtherErr>&&, _Tp> //
    && !is_convertible_v<const expected<_Up, _OtherErr>&, _Tp>
    && !is_convertible_v<const expected<_Up, _OtherErr>&&, _Tp>
    && !is_constructible_v<unexpected<_Err>, expected<_Up, _OtherErr>&>
    && !is_constructible_v<unexpected<_Err>, expected<_Up, _OtherErr>>
    && !is_constructible_v<unexpected<_Err>, const expected<_Up, _OtherErr>&>
    && !is_constructible_v<unexpected<_Err>, const expected<_Up, _OtherErr>>;

public:
  _CCCL_TEMPLATE(class _Up, class _OtherErr)
  _CCCL_REQUIRES(__can_convert<_Up, _OtherErr, const _Up&, const _OtherErr&> _CCCL_AND
                   is_convertible_v<const _Up&, _Tp> _CCCL_AND is_convertible_v<const _OtherErr&, _Err>)
  _CCCL_API inline _CCCL_CONSTEXPR_CXX20 expected(const expected<_Up, _OtherErr>& __other) noexcept(
    is_nothrow_constructible_v<_Tp, const _Up&> && is_nothrow_constructible_v<_Err, const _OtherErr&>) // strengthened
      : __base(__other.__has_val_)
  {
    if (__other.__has_val_)
    {
      ::cuda::std::__construct_at(::cuda::std::addressof(this->__union_.__val_), __other.__union_.__val_);
    }
    else
    {
      ::cuda::std::__construct_at(::cuda::std::addressof(this->__union_.__unex_), __other.__union_.__unex_);
    }
  }

  _CCCL_TEMPLATE(class _Up, class _OtherErr)
  _CCCL_REQUIRES(__can_convert<_Up, _OtherErr, const _Up&, const _OtherErr&> _CCCL_AND(
    !is_convertible_v<const _Up&, _Tp> || !is_convertible_v<const _OtherErr&, _Err>))
  _CCCL_API inline _CCCL_CONSTEXPR_CXX20 explicit expected(const expected<_Up, _OtherErr>& __other) noexcept(
    is_nothrow_constructible_v<_Tp, const _Up&> && is_nothrow_constructible_v<_Err, const _OtherErr&>) // strengthened
      : __base(__other.__has_val_)
  {
    if (__other.__has_val_)
    {
      ::cuda::std::__construct_at(::cuda::std::addressof(this->__union_.__val_), __other.__union_.__val_);
    }
    else
    {
      ::cuda::std::__construct_at(::cuda::std::addressof(this->__union_.__unex_), __other.__union_.__unex_);
    }
  }

  _CCCL_TEMPLATE(class _Up, class _OtherErr)
  _CCCL_REQUIRES(__can_convert<_Up, _OtherErr, _Up, _OtherErr> _CCCL_AND is_convertible_v<_Up, _Tp> _CCCL_AND
                   is_convertible_v<_OtherErr, _Err>)
  _CCCL_API inline _CCCL_CONSTEXPR_CXX20 expected(expected<_Up, _OtherErr>&& __other) noexcept(
    is_nothrow_constructible_v<_Tp, _Up> && is_nothrow_constructible_v<_Err, _OtherErr>) // strengthened
      : __base(__other.__has_val_)
  {
    if (__other.__has_val_)
    {
      ::cuda::std::__construct_at(
        ::cuda::std::addressof(this->__union_.__val_), ::cuda::std::move(__other.__union_.__val_));
    }
    else
    {
      ::cuda::std::__construct_at(
        ::cuda::std::addressof(this->__union_.__unex_), ::cuda::std::move(__other.__union_.__unex_));
    }
  }

  _CCCL_TEMPLATE(class _Up, class _OtherErr)
  _CCCL_REQUIRES(__can_convert<_Up, _OtherErr, _Up, _OtherErr> _CCCL_AND(
    !is_convertible_v<_Up, _Tp> || !is_convertible_v<_OtherErr, _Err>))
  _CCCL_API inline _CCCL_CONSTEXPR_CXX20 explicit expected(expected<_Up, _OtherErr>&& __other) noexcept(
    is_nothrow_constructible_v<_Tp, _Up> && is_nothrow_constructible_v<_Err, _OtherErr>) // strengthened
      : __base(__other.__has_val_)
  {
    if (__other.__has_val_)
    {
      ::cuda::std::__construct_at(
        ::cuda::std::addressof(this->__union_.__val_), ::cuda::std::move(__other.__union_.__val_));
    }
    else
    {
      ::cuda::std::__construct_at(
        ::cuda::std::addressof(this->__union_.__unex_), ::cuda::std::move(__other.__union_.__unex_));
    }
  }

  _CCCL_TEMPLATE(class _Up = _Tp)
  _CCCL_REQUIRES((!is_same_v<remove_cvref_t<_Up>, in_place_t>) _CCCL_AND(!is_same_v<expected, remove_cvref_t<_Up>>)
                   _CCCL_AND(!__unexpected::__is_unexpected<remove_cvref_t<_Up>>)
                     _CCCL_AND is_constructible_v<_Tp, _Up> _CCCL_AND is_convertible_v<_Up, _Tp>)
  _CCCL_API constexpr expected(_Up&& __u) noexcept(is_nothrow_constructible_v<_Tp, _Up>) // strengthened
      : __base(in_place, ::cuda::std::forward<_Up>(__u))
  {}

  _CCCL_TEMPLATE(class _Up = _Tp)
  _CCCL_REQUIRES((!is_same_v<remove_cvref_t<_Up>, in_place_t>) _CCCL_AND(!is_same_v<expected, remove_cvref_t<_Up>>)
                   _CCCL_AND(!__unexpected::__is_unexpected<remove_cvref_t<_Up>>)
                     _CCCL_AND is_constructible_v<_Tp, _Up> _CCCL_AND(!is_convertible_v<_Up, _Tp>))
  _CCCL_API constexpr explicit expected(_Up&& __u) noexcept(is_nothrow_constructible_v<_Tp, _Up>) // strengthened
      : __base(in_place, ::cuda::std::forward<_Up>(__u))
  {}

  _CCCL_TEMPLATE(class _OtherErr)
  _CCCL_REQUIRES(is_constructible_v<_Err, const _OtherErr&> _CCCL_AND is_convertible_v<const _OtherErr&, _Err>)
  _CCCL_API constexpr expected(const unexpected<_OtherErr>& __unex) noexcept(
    is_nothrow_constructible_v<_Err, const _OtherErr&>) // strengthened
      : __base(unexpect, __unex.error())
  {}

  _CCCL_TEMPLATE(class _OtherErr)
  _CCCL_REQUIRES(is_constructible_v<_Err, const _OtherErr&> _CCCL_AND(!is_convertible_v<const _OtherErr&, _Err>))
  _CCCL_API constexpr explicit expected(const unexpected<_OtherErr>& __unex) noexcept(
    is_nothrow_constructible_v<_Err, const _OtherErr&>) // strengthened
      : __base(unexpect, __unex.error())
  {}

  _CCCL_TEMPLATE(class _OtherErr)
  _CCCL_REQUIRES(is_constructible_v<_Err, _OtherErr> _CCCL_AND is_convertible_v<_OtherErr, _Err>)
  _CCCL_API constexpr expected(unexpected<_OtherErr>&& __unex) noexcept(
    is_nothrow_constructible_v<_Err, _OtherErr>) // strengthened
      : __base(unexpect, ::cuda::std::move(__unex.error()))
  {}

  _CCCL_TEMPLATE(class _OtherErr)
  _CCCL_REQUIRES(is_constructible_v<_Err, _OtherErr> _CCCL_AND(!is_convertible_v<_OtherErr, _Err>))
  _CCCL_API constexpr explicit expected(unexpected<_OtherErr>&& __unex) noexcept(
    is_nothrow_constructible_v<_Err, _OtherErr>) // strengthened
      : __base(unexpect, ::cuda::std::move(__unex.error()))
  {}

  _CCCL_TEMPLATE(class... _Args)
  _CCCL_REQUIRES(is_constructible_v<_Tp, _Args...>)
  _CCCL_API constexpr explicit expected(in_place_t, _Args&&... __args) noexcept(
    is_nothrow_constructible_v<_Tp, _Args...>) // strengthened
      : __base(in_place, ::cuda::std::forward<_Args>(__args)...)
  {}

  _CCCL_TEMPLATE(class _Up, class... _Args)
  _CCCL_REQUIRES(is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>)
  _CCCL_API constexpr explicit expected(in_place_t, initializer_list<_Up> __il, _Args&&... __args) noexcept(
    is_nothrow_constructible_v<_Tp, initializer_list<_Up>&, _Args...>) // strengthened
      : __base(in_place, __il, ::cuda::std::forward<_Args>(__args)...)
  {}

  _CCCL_TEMPLATE(class... _Args)
  _CCCL_REQUIRES(is_constructible_v<_Err, _Args...>)
  _CCCL_API constexpr explicit expected(unexpect_t, _Args&&... __args) noexcept(
    is_nothrow_constructible_v<_Err, _Args...>) // strengthened
      : __base(unexpect, ::cuda::std::forward<_Args>(__args)...)
  {}

  _CCCL_TEMPLATE(class _Up, class... _Args)
  _CCCL_REQUIRES(is_constructible_v<_Err, initializer_list<_Up>&, _Args...>)
  _CCCL_API constexpr explicit expected(unexpect_t, initializer_list<_Up> __il, _Args&&... __args) noexcept(
    is_nothrow_constructible_v<_Err, initializer_list<_Up>&, _Args...>) // strengthened
      : __base(unexpect, __il, ::cuda::std::forward<_Args>(__args)...)
  {}

private:
  template <class _Fun, class... _Args>
  _CCCL_API constexpr expected(
    __expected_construct_from_invoke_tag,
    in_place_t,
    _Fun&& __fun,
    _Args&&... __args) noexcept(is_nothrow_constructible_v<_Tp, invoke_result_t<_Fun, _Args...>>)
      : __base(__expected_construct_from_invoke_tag{},
               in_place,
               ::cuda::std::forward<_Fun>(__fun),
               ::cuda::std::forward<_Args>(__args)...)
  {}

  template <class _Fun, class... _Args>
  _CCCL_API constexpr expected(
    __expected_construct_from_invoke_tag,
    unexpect_t,
    _Fun&& __fun,
    _Args&&... __args) noexcept(is_nothrow_constructible_v<_Err, invoke_result_t<_Fun, _Args...>>)
      : __base(__expected_construct_from_invoke_tag{},
               unexpect,
               ::cuda::std::forward<_Fun>(__fun),
               ::cuda::std::forward<_Args>(__args)...)
  {}

public:
  // [expected.object.assign], assignment
  _CCCL_EXEC_CHECK_DISABLE
  _CCCL_TEMPLATE(class _Up = _Tp)
  _CCCL_REQUIRES(
    (!is_same_v<expected, remove_cvref_t<_Up>>) _CCCL_AND(!__unexpected::__is_unexpected<remove_cvref_t<_Up>>)
      _CCCL_AND is_constructible_v<_Tp, _Up> _CCCL_AND is_assignable_v<_Tp&, _Up> _CCCL_AND(
        is_nothrow_constructible_v<_Tp, _Up> || is_nothrow_move_constructible_v<_Tp>
        || is_nothrow_move_constructible_v<_Err>))
  _CCCL_API inline _CCCL_CONSTEXPR_CXX20 expected& operator=(_Up&& __v)
  {
    if (this->__has_val_)
    {
      this->__union_.__val_ = ::cuda::std::forward<_Up>(__v);
    }
    else
    {
      this->__reinit_expected(this->__union_.__val_, this->__union_.__unex_, ::cuda::std::forward<_Up>(__v));
      this->__has_val_ = true;
    }
    return *this;
  }

private:
  template <class _OtherErrQual>
  static constexpr bool __can_assign_from_unexpected =
    is_constructible_v<_Err, _OtherErrQual> && is_assignable_v<_Err&, _OtherErrQual>
    && (is_nothrow_constructible_v<_Err, _OtherErrQual> || is_nothrow_move_constructible_v<_Tp>
        || is_nothrow_move_constructible_v<_Err>);

public:
  _CCCL_EXEC_CHECK_DISABLE
  _CCCL_TEMPLATE(class _OtherErr)
  _CCCL_REQUIRES(__can_assign_from_unexpected<const _OtherErr&>)
  _CCCL_API inline _CCCL_CONSTEXPR_CXX20 expected& operator=(const unexpected<_OtherErr>& __un)
  {
    if (this->__has_val_)
    {
      this->__reinit_expected(this->__union_.__unex_, this->__union_.__val_, __un.error());
      this->__has_val_ = false;
    }
    else
    {
      this->__union_.__unex_ = __un.error();
    }
    return *this;
  }

  _CCCL_EXEC_CHECK_DISABLE
  _CCCL_TEMPLATE(class _OtherErr)
  _CCCL_REQUIRES(__can_assign_from_unexpected<_OtherErr>)
  _CCCL_API inline _CCCL_CONSTEXPR_CXX20 expected& operator=(unexpected<_OtherErr>&& __un)
  {
    if (this->__has_val_)
    {
      this->__reinit_expected(this->__union_.__unex_, this->__union_.__val_, ::cuda::std::move(__un.error()));
      this->__has_val_ = false;
    }
    else
    {
      this->__union_.__unex_ = ::cuda::std::move(__un.error());
    }
    return *this;
  }

  _CCCL_TEMPLATE(class... _Args)
  _CCCL_REQUIRES(is_nothrow_constructible_v<_Tp, _Args...>)
  _CCCL_API inline _CCCL_CONSTEXPR_CXX20 _Tp& emplace(_Args&&... __args) noexcept
  {
    if (this->__has_val_)
    {
      ::cuda::std::__destroy_at(::cuda::std::addressof(this->__union_.__val_));
    }
    else
    {
      ::cuda::std::__destroy_at(::cuda::std::addressof(this->__union_.__unex_));
      this->__has_val_ = true;
    }
    return *::cuda::std::__construct_at(
      ::cuda::std::addressof(this->__union_.__val_), ::cuda::std::forward<_Args>(__args)...);
  }

  _CCCL_TEMPLATE(class _Up, class... _Args)
  _CCCL_REQUIRES(is_nothrow_constructible_v<_Tp, initializer_list<_Up>&, _Args...>)
  _CCCL_API inline _CCCL_CONSTEXPR_CXX20 _Tp& emplace(initializer_list<_Up> __il, _Args&&... __args) noexcept
  {
    if (this->__has_val_)
    {
      ::cuda::std::__destroy_at(::cuda::std::addressof(this->__union_.__val_));
    }
    else
    {
      ::cuda::std::__destroy_at(::cuda::std::addressof(this->__union_.__unex_));
      this->__has_val_ = true;
    }
    return *::cuda::std::__construct_at(
      ::cuda::std::addressof(this->__union_.__val_), __il, ::cuda::std::forward<_Args>(__args)...);
  }

public:
  // [expected.object.swap], swap
  _CCCL_TEMPLATE(class _Tp2 = _Tp, class _Err2 = _Err)
  _CCCL_REQUIRES(__expected::__can_swap<_Tp2, _Err2>)
  _CCCL_API inline _CCCL_CONSTEXPR_CXX20 void swap(expected<_Tp2, _Err>& __rhs) noexcept(
    is_nothrow_move_constructible_v<_Tp2> && is_nothrow_swappable_v<_Tp2> && is_nothrow_move_constructible_v<_Err>
    && is_nothrow_swappable_v<_Err>)
  {
    if (this->__has_val_)
    {
      if (__rhs.__has_val_)
      {
        using ::cuda::std::swap;
        swap(this->__union_.__val_, __rhs.__union_.__val_);
      }
      else
      {
        this->__swap_val_unex_impl(*this, __rhs);
      }
    }
    else
    {
      if (__rhs.__has_val_)
      {
        this->__swap_val_unex_impl(__rhs, *this);
      }
      else
      {
        using ::cuda::std::swap;
        swap(this->__union_.__unex_, __rhs.__union_.__unex_);
      }
    }
  }

  template <class _Tp2 = _Tp, class _Err2 = _Err>
  friend _CCCL_API inline _CCCL_CONSTEXPR_CXX20 auto swap(expected& __x, expected& __y) noexcept(
    is_nothrow_move_constructible_v<_Tp2> && is_nothrow_swappable_v<_Tp2> && is_nothrow_move_constructible_v<_Err2>
    && is_nothrow_swappable_v<_Err2>) _CCCL_TRAILING_REQUIRES(void)(__expected::__can_swap<_Tp2, _Err2>)
  {
    return __x.swap(__y); // some compiler warn about non void function without return
  }

  // [expected.object.obs], observers
  _CCCL_API constexpr const _Tp* operator->() const noexcept
  {
    _CCCL_ASSERT(this->__has_val_, "expected::operator-> requires the expected to contain a value");
    return ::cuda::std::addressof(this->__union_.__val_);
  }

  _CCCL_API constexpr _Tp* operator->() noexcept
  {
    _CCCL_ASSERT(this->__has_val_, "expected::operator-> requires the expected to contain a value");
    return ::cuda::std::addressof(this->__union_.__val_);
  }

  _CCCL_API constexpr const _Tp& operator*() const& noexcept
  {
    _CCCL_ASSERT(this->__has_val_, "expected::operator* requires the expected to contain a value");
    return this->__union_.__val_;
  }

  _CCCL_API constexpr _Tp& operator*() & noexcept
  {
    _CCCL_ASSERT(this->__has_val_, "expected::operator* requires the expected to contain a value");
    return this->__union_.__val_;
  }

  _CCCL_API constexpr const _Tp&& operator*() const&& noexcept
  {
    _CCCL_ASSERT(this->__has_val_, "expected::operator* requires the expected to contain a value");
    return ::cuda::std::move(this->__union_.__val_);
  }

  _CCCL_API constexpr _Tp&& operator*() && noexcept
  {
    _CCCL_ASSERT(this->__has_val_, "expected::operator* requires the expected to contain a value");
    return ::cuda::std::move(this->__union_.__val_);
  }

  _CCCL_API constexpr explicit operator bool() const noexcept
  {
    return this->__has_val_;
  }

  _CCCL_API constexpr bool has_value() const noexcept
  {
    return this->__has_val_;
  }

  _CCCL_API constexpr const _Tp& value() const&
  {
    static_assert(is_copy_constructible_v<_Err>, "expected::value() const& requires is_copy_constructible_v<E>");
    if (!this->__has_val_)
    {
      __throw_bad_expected_access<_Err>(this->__union_.__unex_);
    }
    return this->__union_.__val_;
  }

  _CCCL_API constexpr _Tp& value() &
  {
    static_assert(is_copy_constructible_v<_Err>, "expected::value() & requires is_copy_constructible_v<E>");
    if (!this->__has_val_)
    {
      __throw_bad_expected_access<_Err>(::cuda::std::as_const(this->__union_.__unex_));
    }
    return this->__union_.__val_;
  }

  _CCCL_API constexpr const _Tp&& value() const&&
  {
    static_assert(is_copy_constructible_v<_Err>, "expected::value() const&& requires is_copy_constructible_v<E>");
    static_assert(is_constructible_v<_Err, decltype(::cuda::std::move(error()))>,
                  "expected::value() const&& requires is_constructible_v<E, decltype(::cuda::std::move(error()))>");
    if (!this->__has_val_)
    {
      __throw_bad_expected_access<_Err>(::cuda::std::move(this->__union_.__unex_));
    }
    return ::cuda::std::move(this->__union_.__val_);
  }

  _CCCL_API constexpr _Tp&& value() &&
  {
    static_assert(is_copy_constructible_v<_Err>, "expected::value() && requires is_copy_constructible_v<E>");
    static_assert(is_constructible_v<_Err, decltype(::cuda::std::move(error()))>,
                  "expected::value() && requires is_constructible_v<E, decltype(::cuda::std::move(error()))>");
    if (!this->__has_val_)
    {
      __throw_bad_expected_access<_Err>(::cuda::std::move(this->__union_.__unex_));
    }
    return ::cuda::std::move(this->__union_.__val_);
  }

  _CCCL_API constexpr const _Err& error() const& noexcept
  {
    _CCCL_ASSERT(!this->__has_val_, "expected::error requires the expected to contain an error");
    return this->__union_.__unex_;
  }

  _CCCL_API constexpr _Err& error() & noexcept
  {
    _CCCL_ASSERT(!this->__has_val_, "expected::error requires the expected to contain an error");
    return this->__union_.__unex_;
  }

  _CCCL_API constexpr const _Err&& error() const&& noexcept
  {
    _CCCL_ASSERT(!this->__has_val_, "expected::error requires the expected to contain an error");
    return ::cuda::std::move(this->__union_.__unex_);
  }

  _CCCL_API constexpr _Err&& error() && noexcept
  {
    _CCCL_ASSERT(!this->__has_val_, "expected::error requires the expected to contain an error");
    return ::cuda::std::move(this->__union_.__unex_);
  }

  template <class _Up>
  _CCCL_API constexpr _Tp value_or(_Up&& __v) const&
  {
    static_assert(is_copy_constructible_v<_Tp>, "value_type has to be copy constructible");
    static_assert(is_convertible_v<_Up, _Tp>, "argument has to be convertible to value_type");
    return this->__has_val_ ? this->__union_.__val_ : static_cast<_Tp>(::cuda::std::forward<_Up>(__v));
  }

  template <class _Up>
  _CCCL_API constexpr _Tp value_or(_Up&& __v) &&
  {
    static_assert(is_move_constructible_v<_Tp>, "value_type has to be move constructible");
    static_assert(is_convertible_v<_Up, _Tp>, "argument has to be convertible to value_type");
    return this->__has_val_ ? ::cuda::std::move(this->__union_.__val_)
                            : static_cast<_Tp>(::cuda::std::forward<_Up>(__v));
  }

  // [expected.object.monadic]
  _CCCL_TEMPLATE(class _Fun, class _Err2 = _Err)
  _CCCL_REQUIRES(is_constructible_v<_Err2, _Err2&>)
  _CCCL_API constexpr auto and_then(_Fun&& __fun) &
  {
    using _Res = remove_cvref_t<invoke_result_t<_Fun, _Tp&>>;

    static_assert(__expected::__is_expected<_Res>, "Result of f(value()) must be a specialization of std::expected");
    static_assert(is_same_v<typename _Res::error_type, _Err>,
                  "The error type of the result of f(value()) must be the same as that of std::expected");

    if (this->__has_val_)
    {
      return ::cuda::std::invoke(::cuda::std::forward<_Fun>(__fun), this->__union_.__val_);
    }
    else
    {
      return _Res{unexpect, this->__union_.__unex_};
    }
  }

  _CCCL_TEMPLATE(class _Fun, class _Err2 = _Err)
  _CCCL_REQUIRES(is_copy_constructible_v<_Err2>)
  _CCCL_API constexpr auto and_then(_Fun&& __fun) const&
  {
    using _Res = remove_cvref_t<invoke_result_t<_Fun, const _Tp&>>;

    static_assert(__expected::__is_expected<_Res>, "Result of f(value()) must be a specialization of std::expected");
    static_assert(is_same_v<typename _Res::error_type, _Err>,
                  "The error type of the result of f(value()) must be the same as that of std::expected");

    if (this->__has_val_)
    {
      return ::cuda::std::invoke(::cuda::std::forward<_Fun>(__fun), this->__union_.__val_);
    }
    else
    {
      return _Res{unexpect, this->__union_.__unex_};
    }
  }

  _CCCL_TEMPLATE(class _Fun, class _Err2 = _Err)
  _CCCL_REQUIRES(is_move_constructible_v<_Err2>)
  _CCCL_API constexpr auto and_then(_Fun&& __fun) &&
  {
    using _Res = remove_cvref_t<invoke_result_t<_Fun, _Tp>>;

    static_assert(__expected::__is_expected<_Res>, "Result of f(value()) must be a specialization of std::expected");
    static_assert(is_same_v<typename _Res::error_type, _Err>,
                  "The error type of the result of f(value()) must be the same as that of std::expected");

    if (this->__has_val_)
    {
      return ::cuda::std::invoke(::cuda::std::forward<_Fun>(__fun), ::cuda::std::move(this->__union_.__val_));
    }
    else
    {
      return _Res{unexpect, ::cuda::std::move(this->__union_.__unex_)};
    }
  }

  _CCCL_TEMPLATE(class _Fun, class _Err2 = _Err)
  _CCCL_REQUIRES(is_constructible_v<_Err2, const _Err2>)
  _CCCL_API constexpr auto and_then(_Fun&& __fun) const&&
  {
    using _Res = remove_cvref_t<invoke_result_t<_Fun, const _Tp>>;

    static_assert(__expected::__is_expected<_Res>, "Result of f(value()) must be a specialization of std::expected");
    static_assert(is_same_v<typename _Res::error_type, _Err>,
                  "The error type of the result of f(value()) must be the same as that of std::expected");

    if (this->__has_val_)
    {
      return ::cuda::std::invoke(::cuda::std::forward<_Fun>(__fun), ::cuda::std::move(this->__union_.__val_));
    }
    else
    {
      return _Res{unexpect, ::cuda::std::move(this->__union_.__unex_)};
    }
  }

  _CCCL_TEMPLATE(class _Fun, class _Tp2 = _Tp)
  _CCCL_REQUIRES(is_constructible_v<_Tp2, _Tp2&>)
  _CCCL_API constexpr auto or_else(_Fun&& __fun) &
  {
    using _Res = remove_cvref_t<invoke_result_t<_Fun, _Err&>>;

    static_assert(__expected::__is_expected<_Res>,
                  "Result of std::expected::or_else must be a specialization of std::expected");
    static_assert(is_same_v<typename _Res::value_type, _Tp>,
                  "The value type of the result of std::expected::or_else must be the same as that of std::expected");

    if (this->__has_val_)
    {
      return _Res{in_place, this->__union_.__val_};
    }
    else
    {
      return ::cuda::std::invoke(::cuda::std::forward<_Fun>(__fun), this->__union_.__unex_);
    }
  }

  _CCCL_TEMPLATE(class _Fun, class _Tp2 = _Tp)
  _CCCL_REQUIRES(is_copy_constructible_v<_Tp2>)
  _CCCL_API constexpr auto or_else(_Fun&& __fun) const&
  {
    using _Res = remove_cvref_t<invoke_result_t<_Fun, const _Err&>>;

    static_assert(__expected::__is_expected<_Res>,
                  "Result of std::expected::or_else must be a specialization of std::expected");
    static_assert(is_same_v<typename _Res::value_type, _Tp>,
                  "The value type of the result of std::expected::or_else must be the same as that of std::expected");

    if (this->__has_val_)
    {
      return _Res{in_place, this->__union_.__val_};
    }
    else
    {
      return ::cuda::std::invoke(::cuda::std::forward<_Fun>(__fun), this->__union_.__unex_);
    }
  }

  _CCCL_TEMPLATE(class _Fun, class _Tp2 = _Tp)
  _CCCL_REQUIRES(is_move_constructible_v<_Tp2>)
  _CCCL_API constexpr auto or_else(_Fun&& __fun) &&
  {
    using _Res = remove_cvref_t<invoke_result_t<_Fun, _Err>>;

    static_assert(__expected::__is_expected<_Res>,
                  "Result of std::expected::or_else must be a specialization of std::expected");
    static_assert(is_same_v<typename _Res::value_type, _Tp>,
                  "The value type of the result of std::expected::or_else must be the same as that of std::expected");

    if (this->__has_val_)
    {
      return _Res{in_place, ::cuda::std::move(this->__union_.__val_)};
    }
    else
    {
      return ::cuda::std::invoke(::cuda::std::forward<_Fun>(__fun), ::cuda::std::move(this->__union_.__unex_));
    }
  }

  _CCCL_TEMPLATE(class _Fun, class _Tp2 = _Tp)
  _CCCL_REQUIRES(is_constructible_v<_Tp2, const _Tp2>)
  _CCCL_API constexpr auto or_else(_Fun&& __fun) const&&
  {
    using _Res = remove_cvref_t<invoke_result_t<_Fun, const _Err>>;

    static_assert(__expected::__is_expected<_Res>,
                  "Result of std::expected::or_else must be a specialization of std::expected");
    static_assert(is_same_v<typename _Res::value_type, _Tp>,
                  "The value type of the result of std::expected::or_else must be the same as that of std::expected");

    if (this->__has_val_)
    {
      return _Res{in_place, ::cuda::std::move(this->__union_.__val_)};
    }
    else
    {
      return ::cuda::std::invoke(::cuda::std::forward<_Fun>(__fun), ::cuda::std::move(this->__union_.__unex_));
    }
  }

  _CCCL_TEMPLATE(class _Fun, class _Tp2 = _Tp, class _Err2 = _Err)
  _CCCL_REQUIRES(is_constructible_v<_Err2, _Err2&> _CCCL_AND is_same_v<remove_cv_t<invoke_result_t<_Fun, _Tp2&>>, void>)
  _CCCL_API constexpr auto transform(_Fun&& __fun) &
  {
    static_assert(invocable<_Fun, _Tp&>, "std::expected::transform requires that F must be invocable with T.");
    using _Res = remove_cv_t<invoke_result_t<_Fun, _Tp&>>;

    if (this->__has_val_)
    {
      ::cuda::std::invoke(::cuda::std::forward<_Fun>(__fun), this->__union_.__val_);
      return expected<void, _Err>{};
    }
    else
    {
      return expected<_Res, _Err>{unexpect, this->__union_.__unex_};
    }
  }

  _CCCL_TEMPLATE(class _Fun, class _Tp2 = _Tp, class _Err2 = _Err)
  _CCCL_REQUIRES(
    is_constructible_v<_Err2, _Err2&> _CCCL_AND(!is_same_v<remove_cv_t<invoke_result_t<_Fun, _Tp2&>>, void>))
  _CCCL_API constexpr auto transform(_Fun&& __fun) &
  {
    static_assert(invocable<_Fun, _Tp&>, "std::expected::transform requires that F must be invocable with T.");
    using _Res = remove_cv_t<invoke_result_t<_Fun, _Tp&>>;

    static_assert(__invoke_constructible<_Fun, _Tp&>,
                  "std::expected::transform requires that the return type of F is constructible with the result of "
                  "invoking F");
    static_assert(__expected::__valid_expected<_Res, _Err>,
                  "std::expected::transform requires that the return type of F must be a valid argument for "
                  "std::expected");

    if (this->__has_val_)
    {
      return expected<_Res, _Err>{
        __expected_construct_from_invoke_tag{}, in_place, ::cuda::std::forward<_Fun>(__fun), this->__union_.__val_};
    }
    else
    {
      return expected<_Res, _Err>{unexpect, this->__union_.__unex_};
    }
  }

  _CCCL_TEMPLATE(class _Fun, class _Tp2 = _Tp, class _Err2 = _Err)
  _CCCL_REQUIRES(
    is_copy_constructible_v<_Err2> _CCCL_AND is_same_v<remove_cv_t<invoke_result_t<_Fun, const _Tp2&>>, void>)
  _CCCL_API constexpr auto transform(_Fun&& __fun) const&
  {
    static_assert(invocable<_Fun, const _Tp&>, "std::expected::transform requires that F must be invocable with T.");
    using _Res = remove_cv_t<invoke_result_t<_Fun, const _Tp&>>;

    if (this->__has_val_)
    {
      ::cuda::std::invoke(::cuda::std::forward<_Fun>(__fun), this->__union_.__val_);
      return expected<_Res, _Err>{};
    }
    else
    {
      return expected<_Res, _Err>{unexpect, this->__union_.__unex_};
    }
  }

  _CCCL_TEMPLATE(class _Fun, class _Tp2 = _Tp, class _Err2 = _Err)
  _CCCL_REQUIRES(
    is_copy_constructible_v<_Err2> _CCCL_AND(!is_same_v<remove_cv_t<invoke_result_t<_Fun, const _Tp2&>>, void>))
  _CCCL_API constexpr auto transform(_Fun&& __fun) const&
  {
    static_assert(invocable<_Fun, const _Tp&>, "std::expected::transform requires that F must be invocable with T");
    using _Res = remove_cv_t<invoke_result_t<_Fun, const _Tp&>>;

    static_assert(__invoke_constructible<_Fun, const _Tp&>,
                  "std::expected::transform requires that the return type of F is constructible with the result of "
                  "invoking F");
    static_assert(__expected::__valid_expected<_Res, _Err>,
                  "std::expected::transform requires that the return type of F must be a valid argument for "
                  "std::expected");

    if (this->__has_val_)
    {
      return expected<_Res, _Err>{
        __expected_construct_from_invoke_tag{}, in_place, ::cuda::std::forward<_Fun>(__fun), this->__union_.__val_};
    }
    else
    {
      return expected<_Res, _Err>{unexpect, this->__union_.__unex_};
    }
  }

  _CCCL_TEMPLATE(class _Fun, class _Tp2 = _Tp, class _Err2 = _Err)
  _CCCL_REQUIRES(is_move_constructible_v<_Err2> _CCCL_AND is_same_v<remove_cv_t<invoke_result_t<_Fun, _Tp2>>, void>)
  _CCCL_API constexpr auto transform(_Fun&& __fun) &&
  {
    static_assert(invocable<_Fun, _Tp>, "std::expected::transform requires that F must be invocable with T.");
    using _Res = remove_cv_t<invoke_result_t<_Fun, _Tp>>;

    if (this->__has_val_)
    {
      ::cuda::std::invoke(::cuda::std::forward<_Fun>(__fun), ::cuda::std::move(this->__union_.__val_));
      return expected<_Res, _Err>{};
    }
    else
    {
      return expected<_Res, _Err>{unexpect, ::cuda::std::move(this->__union_.__unex_)};
    }
  }
  _CCCL_TEMPLATE(class _Fun, class _Tp2 = _Tp, class _Err2 = _Err)
  _CCCL_REQUIRES(is_move_constructible_v<_Err2> _CCCL_AND(!is_same_v<remove_cv_t<invoke_result_t<_Fun, _Tp2>>, void>))
  _CCCL_API constexpr auto transform(_Fun&& __fun) &&
  {
    static_assert(invocable<_Fun, _Tp>, "std::expected::transform requires that F must be invocable with T");
    using _Res = remove_cv_t<invoke_result_t<_Fun, _Tp>>;

    static_assert(__invoke_constructible<_Fun, _Tp>,
                  "std::expected::transform requires that the return type of F is constructible with the result of "
                  "invoking F");
    static_assert(__expected::__valid_expected<_Res, _Err>,
                  "std::expected::transform requires that the return type of F must be a valid argument for "
                  "std::expected");

    if (this->__has_val_)
    {
      return expected<_Res, _Err>{
        __expected_construct_from_invoke_tag{},
        in_place,
        ::cuda::std::forward<_Fun>(__fun),
        ::cuda::std::move(this->__union_.__val_)};
    }
    else
    {
      return expected<_Res, _Err>{unexpect, ::cuda::std::move(this->__union_.__unex_)};
    }
  }

  _CCCL_TEMPLATE(class _Fun, class _Tp2 = _Tp, class _Err2 = _Err)
  _CCCL_REQUIRES(
    is_constructible_v<_Err2, const _Err2> _CCCL_AND is_same_v<remove_cv_t<invoke_result_t<_Fun, const _Tp2>>, void>)
  _CCCL_API constexpr auto transform(_Fun&& __fun) const&&
  {
    static_assert(invocable<_Fun, const _Tp>, "std::expected::transform requires that F must be invocable with T.");
    using _Res = remove_cv_t<invoke_result_t<_Fun, const _Tp>>;

    if (this->__has_val_)
    {
      ::cuda::std::invoke(::cuda::std::forward<_Fun>(__fun), ::cuda::std::move(this->__union_.__val_));
      return expected<_Res, _Err>{};
    }
    else
    {
      return expected<_Res, _Err>{unexpect, ::cuda::std::move(this->__union_.__unex_)};
    }
  }

  _CCCL_TEMPLATE(class _Fun, class _Tp2 = _Tp, class _Err2 = _Err)
  _CCCL_REQUIRES(
    is_constructible_v<_Err2, const _Err2> _CCCL_AND(!is_same_v<remove_cv_t<invoke_result_t<_Fun, const _Tp2>>, void>))
  _CCCL_API constexpr auto transform(_Fun&& __fun) const&&
  {
    static_assert(invocable<_Fun, const _Tp>, "std::expected::transform requires that F must be invocable with T");
    using _Res = remove_cv_t<invoke_result_t<_Fun, const _Tp>>;

    static_assert(__invoke_constructible<_Fun, const _Tp>,
                  "std::expected::transform requires that the return type of F is constructible with the result of "
                  "invoking F");
    static_assert(__expected::__valid_expected<_Res, _Err>,
                  "std::expected::transform requires that the return type of F must be a valid argument for "
                  "std::expected");

    if (this->__has_val_)
    {
      return expected<_Res, _Err>{
        __expected_construct_from_invoke_tag{},
        in_place,
        ::cuda::std::forward<_Fun>(__fun),
        ::cuda::std::move(this->__union_.__val_)};
    }
    else
    {
      return expected<_Res, _Err>{unexpect, ::cuda::std::move(this->__union_.__unex_)};
    }
  }

  _CCCL_TEMPLATE(class _Fun, class _Tp2 = _Tp)
  _CCCL_REQUIRES(is_constructible_v<_Tp2, _Tp2&>)
  _CCCL_API constexpr auto transform_error(_Fun&& __fun) &
  {
    static_assert(invocable<_Fun, _Err&>, "std::expected::transform_error requires that F must be invocable with E");
    using _Res = remove_cv_t<invoke_result_t<_Fun, _Err&>>;

    static_assert(__invoke_constructible<_Fun, _Err&>,
                  "std::expected::transform_error requires that the return type of F is constructible with the result "
                  "of invoking F");
    static_assert(__expected::__valid_expected<_Tp, _Res>,
                  "std::expected::transform_error requires that the return type of F must be a valid argument for "
                  "std::expected");

    if (this->__has_val_)
    {
      return expected<_Tp, _Res>{in_place, this->__union_.__val_};
    }
    else
    {
      return expected<_Tp, _Res>{
        __expected_construct_from_invoke_tag{}, unexpect, ::cuda::std::forward<_Fun>(__fun), this->__union_.__unex_};
    }
  }

  _CCCL_TEMPLATE(class _Fun, class _Tp2 = _Tp)
  _CCCL_REQUIRES(is_copy_constructible_v<_Tp2>)
  _CCCL_API constexpr auto transform_error(_Fun&& __fun) const&
  {
    static_assert(invocable<_Fun, const _Err&>,
                  "std::expected::transform_error requires that F must be invocable with E");
    using _Res = remove_cv_t<invoke_result_t<_Fun, const _Err&>>;

    static_assert(__invoke_constructible<_Fun, const _Err&>,
                  "std::expected::transform_error requires that the return type of F is constructible with the result "
                  "of invoking F");
    static_assert(__expected::__valid_expected<_Tp, _Res>,
                  "std::expected::transform_error requires that the return type of F must be a valid argument for "
                  "std::expected");

    if (this->__has_val_)
    {
      return expected<_Tp, _Res>{in_place, this->__union_.__val_};
    }
    else
    {
      return expected<_Tp, _Res>{
        __expected_construct_from_invoke_tag{}, unexpect, ::cuda::std::forward<_Fun>(__fun), this->__union_.__unex_};
    }
  }

  _CCCL_TEMPLATE(class _Fun, class _Tp2 = _Tp)
  _CCCL_REQUIRES(is_move_constructible_v<_Tp2>)
  _CCCL_API constexpr auto transform_error(_Fun&& __fun) &&
  {
    static_assert(invocable<_Fun, _Err>, "std::expected::transform_error requires that F must be invocable with E");
    using _Res = remove_cv_t<invoke_result_t<_Fun, _Err>>;

    static_assert(__invoke_constructible<_Fun, _Err>,
                  "std::expected::transform_error requires that the return type of F is constructible with the result "
                  "of invoking F");
    static_assert(__expected::__valid_expected<_Tp, _Res>,
                  "std::expected::transform_error requires that the return type of F must be a valid argument for "
                  "std::expected");

    if (this->__has_val_)
    {
      return expected<_Tp, _Res>{in_place, ::cuda::std::move(this->__union_.__val_)};
    }
    else
    {
      return expected<_Tp, _Res>{
        __expected_construct_from_invoke_tag{},
        unexpect,
        ::cuda::std::forward<_Fun>(__fun),
        ::cuda::std::move(this->__union_.__unex_)};
    }
  }

  _CCCL_TEMPLATE(class _Fun, class _Tp2 = _Tp)
  _CCCL_REQUIRES(is_constructible_v<_Tp2, const _Tp2>)
  _CCCL_API constexpr auto transform_error(_Fun&& __fun) const&&
  {
    static_assert(invocable<_Fun, const _Err>,
                  "std::expected::transform_error requires that F must be invocable with E");
    using _Res = remove_cv_t<invoke_result_t<_Fun, const _Err>>;

    static_assert(__invoke_constructible<_Fun, const _Err>,
                  "std::expected::transform_error requires that the return type of F is constructible with the result "
                  "of invoking F");
    static_assert(__expected::__valid_expected<_Tp, _Res>,
                  "std::expected::transform_error requires that the return type of F must be a valid argument for "
                  "std::expected");

    if (this->__has_val_)
    {
      return expected<_Tp, _Res>{in_place, ::cuda::std::move(this->__union_.__val_)};
    }
    else
    {
      return expected<_Tp, _Res>{
        __expected_construct_from_invoke_tag{},
        unexpect,
        ::cuda::std::forward<_Fun>(__fun),
        ::cuda::std::move(this->__union_.__unex_)};
    }
  }

  // [expected.object.eq], equality operators
  _CCCL_EXEC_CHECK_DISABLE
  friend _CCCL_API constexpr bool operator==(const expected& __x, const expected& __y)
  {
    if (__x.__has_val_ != __y.has_value())
    {
      return false;
    }
    else
    {
      if (__x.__has_val_)
      {
        return __x.__union_.__val_ == __y.value();
      }
      else
      {
        return __x.__union_.__unex_ == __y.error();
      }
    }
  }

#if _CCCL_STD_VER < 2020
  _CCCL_EXEC_CHECK_DISABLE
  friend _CCCL_API constexpr bool operator!=(const expected& __x, const expected& __y)
  {
    return !(__x == __y);
  }
#endif // _CCCL_STD_VER < 2020

  _CCCL_EXEC_CHECK_DISABLE
  _CCCL_TEMPLATE(class _T2, class _E2)
  _CCCL_REQUIRES((!is_void_v<_T2>) )
  friend _CCCL_API constexpr bool operator==(const expected& __x, const expected<_T2, _E2>& __y)
  {
    if (__x.__has_val_ != __y.has_value())
    {
      return false;
    }
    else
    {
      if (__x.__has_val_)
      {
        return __x.__union_.__val_ == __y.value();
      }
      else
      {
        return __x.__union_.__unex_ == __y.error();
      }
    }
  }

#if _CCCL_STD_VER < 2020
  _CCCL_EXEC_CHECK_DISABLE
  _CCCL_TEMPLATE(class _T2, class _E2)
  _CCCL_REQUIRES((!is_void_v<_T2>) )
  friend _CCCL_API constexpr bool operator!=(const expected& __x, const expected<_T2, _E2>& __y)
  {
    return !(__x == __y);
  }
#endif // _CCCL_STD_VER < 2020

  _CCCL_EXEC_CHECK_DISABLE
  _CCCL_TEMPLATE(class _T2)
  _CCCL_REQUIRES((!__expected::__is_expected_nonvoid<_T2>) )
  friend _CCCL_API constexpr bool operator==(const expected& __x, const _T2& __v)
  {
    return __x.__has_val_ && static_cast<bool>(__x.__union_.__val_ == __v);
  }
#if _CCCL_STD_VER < 2020
  _CCCL_EXEC_CHECK_DISABLE
  _CCCL_TEMPLATE(class _T2)
  _CCCL_REQUIRES((!__expected::__is_expected_nonvoid<_T2>) )
  friend _CCCL_API constexpr bool operator==(const _T2& __v, const expected& __x)
  {
    return __x.__has_val_ && static_cast<bool>(__x.__union_.__val_ == __v);
  }
  _CCCL_EXEC_CHECK_DISABLE
  _CCCL_TEMPLATE(class _T2)
  _CCCL_REQUIRES((!__expected::__is_expected_nonvoid<_T2>) )
  friend _CCCL_API constexpr bool operator!=(const expected& __x, const _T2& __v)
  {
    return !__x.__has_val_ || static_cast<bool>(__x.__union_.__val_ != __v);
  }
  _CCCL_EXEC_CHECK_DISABLE
  _CCCL_TEMPLATE(class _T2)
  _CCCL_REQUIRES((!__expected::__is_expected_nonvoid<_T2>) )
  friend _CCCL_API constexpr bool operator!=(const _T2& __v, const expected& __x)
  {
    return !__x.__has_val_ || static_cast<bool>(__x.__union_.__val_ != __v);
  }
#endif // _CCCL_STD_VER < 2020

  _CCCL_EXEC_CHECK_DISABLE
  template <class _E2>
  friend _CCCL_API constexpr bool operator==(const expected& __x, const unexpected<_E2>& __e)
  {
    return !__x.__has_val_ && static_cast<bool>(__x.__union_.__unex_ == __e.error());
  }
#if _CCCL_STD_VER < 2020
  _CCCL_EXEC_CHECK_DISABLE
  template <class _E2>
  friend _CCCL_API constexpr bool operator==(const unexpected<_E2>& __e, const expected& __x)
  {
    return !__x.__has_val_ && static_cast<bool>(__x.__union_.__unex_ == __e.error());
  }
  _CCCL_EXEC_CHECK_DISABLE
  template <class _E2>
  friend _CCCL_API constexpr bool operator!=(const expected& __x, const unexpected<_E2>& __e)
  {
    return __x.__has_val_ || static_cast<bool>(__x.__union_.__unex_ != __e.error());
  }
  _CCCL_EXEC_CHECK_DISABLE
  template <class _E2>
  friend _CCCL_API constexpr bool operator!=(const unexpected<_E2>& __e, const expected& __x)
  {
    return __x.__has_val_ || static_cast<bool>(__x.__union_.__unex_ != __e.error());
  }
#endif // _CCCL_STD_VER < 2020
};

template <class _Err>
class expected<void, _Err> : private __expected_move_assign<void, _Err>
{
  using __base = __expected_move_assign<void, _Err>;
  static_assert(__unexpected::__valid_unexpected<_Err>,
                "[expected.void.general] A program that instantiates expected<T, E> with a E that is not a "
                "valid argument for unexpected<E> is ill-formed");

  template <class, class>
  friend class expected;

  template <class _Up, class _OtherErr, class _OtherErrQual>
  static constexpr bool __can_convert =
    is_void_v<_Up> && is_constructible_v<_Err, _OtherErrQual>
    && !is_constructible_v<unexpected<_Err>, expected<_Up, _OtherErr>&>
    && !is_constructible_v<unexpected<_Err>, expected<_Up, _OtherErr>>
    && !is_constructible_v<unexpected<_Err>, const expected<_Up, _OtherErr>&>
    && !is_constructible_v<unexpected<_Err>, const expected<_Up, _OtherErr>>;

public:
  using value_type      = void;
  using error_type      = _Err;
  using unexpected_type = unexpected<_Err>;

  template <class _Up>
  using rebind = expected<_Up, error_type>;

  // [expected.void.ctor], constructors
  _CCCL_HIDE_FROM_ABI constexpr expected()                           = default;
  _CCCL_HIDE_FROM_ABI constexpr expected(const expected&)            = default;
  _CCCL_HIDE_FROM_ABI constexpr expected(expected&&)                 = default;
  _CCCL_HIDE_FROM_ABI constexpr expected& operator=(const expected&) = default;
  _CCCL_HIDE_FROM_ABI constexpr expected& operator=(expected&&)      = default;

  _CCCL_TEMPLATE(class _Up, class _OtherErr)
  _CCCL_REQUIRES(__can_convert<_Up, _OtherErr, const _OtherErr&> _CCCL_AND is_convertible_v<const _OtherErr&, _Err>)
  _CCCL_API inline _CCCL_CONSTEXPR_CXX20 expected(const expected<_Up, _OtherErr>& __other) noexcept(
    is_nothrow_constructible_v<_Err, const _OtherErr&>) // strengthened
      : __base(__other.__has_val_)
  {
    if (!__other.__has_val_)
    {
      ::cuda::std::__construct_at(::cuda::std::addressof(this->__union_.__unex_), __other.__union_.__unex_);
    }
  }

  _CCCL_TEMPLATE(class _Up, class _OtherErr)
  _CCCL_REQUIRES(__can_convert<_Up, _OtherErr, const _OtherErr&> _CCCL_AND(!is_convertible_v<const _OtherErr&, _Err>))
  _CCCL_API inline _CCCL_CONSTEXPR_CXX20 explicit expected(const expected<_Up, _OtherErr>& __other) noexcept(
    is_nothrow_constructible_v<_Err, const _OtherErr&>) // strengthened
      : __base(__other.__has_val_)
  {
    if (!__other.__has_val_)
    {
      ::cuda::std::__construct_at(::cuda::std::addressof(this->__union_.__unex_), __other.__union_.__unex_);
    }
  }

  _CCCL_TEMPLATE(class _Up, class _OtherErr)
  _CCCL_REQUIRES(__can_convert<_Up, _OtherErr, _OtherErr> _CCCL_AND is_convertible_v<_OtherErr, _Err>)
  _CCCL_API inline _CCCL_CONSTEXPR_CXX20
  expected(expected<_Up, _OtherErr>&& __other) noexcept(is_nothrow_constructible_v<_Err, _OtherErr>) // strengthened
      : __base(__other.__has_val_)
  {
    if (!__other.__has_val_)
    {
      ::cuda::std::__construct_at(
        ::cuda::std::addressof(this->__union_.__unex_), ::cuda::std::move(__other.__union_.__unex_));
    }
  }

  _CCCL_TEMPLATE(class _Up, class _OtherErr)
  _CCCL_REQUIRES(__can_convert<_Up, _OtherErr, _OtherErr> _CCCL_AND(!is_convertible_v<_OtherErr, _Err>))
  _CCCL_API inline _CCCL_CONSTEXPR_CXX20 explicit expected(expected<_Up, _OtherErr>&& __other) noexcept(
    is_nothrow_constructible_v<_Err, _OtherErr>) // strengthened
      : __base(__other.__has_val_)
  {
    if (!__other.__has_val_)
    {
      ::cuda::std::__construct_at(
        ::cuda::std::addressof(this->__union_.__unex_), ::cuda::std::move(__other.__union_.__unex_));
    }
  }

  _CCCL_TEMPLATE(class _OtherErr)
  _CCCL_REQUIRES(is_constructible_v<_Err, const _OtherErr&> _CCCL_AND is_convertible_v<const _OtherErr&, _Err>)
  _CCCL_API constexpr expected(const unexpected<_OtherErr>& __unex) noexcept(
    is_nothrow_constructible_v<_Err, const _OtherErr&>) // strengthened
      : __base(unexpect, __unex.error())
  {}

  _CCCL_TEMPLATE(class _OtherErr)
  _CCCL_REQUIRES(is_constructible_v<_Err, const _OtherErr&> _CCCL_AND(!is_convertible_v<const _OtherErr&, _Err>))
  _CCCL_API constexpr explicit expected(const unexpected<_OtherErr>& __unex) noexcept(
    is_nothrow_constructible_v<_Err, const _OtherErr&>) // strengthened
      : __base(unexpect, __unex.error())
  {}

  _CCCL_TEMPLATE(class _OtherErr)
  _CCCL_REQUIRES(is_constructible_v<_Err, _OtherErr> _CCCL_AND is_convertible_v<_OtherErr, _Err>)
  _CCCL_API constexpr expected(unexpected<_OtherErr>&& __unex) noexcept(
    is_nothrow_constructible_v<_Err, _OtherErr>) // strengthened
      : __base(unexpect, ::cuda::std::move(__unex.error()))
  {}

  _CCCL_TEMPLATE(class _OtherErr)
  _CCCL_REQUIRES(is_constructible_v<_Err, _OtherErr> _CCCL_AND(!is_convertible_v<_OtherErr, _Err>))
  _CCCL_API constexpr explicit expected(unexpected<_OtherErr>&& __unex) noexcept(
    is_nothrow_constructible_v<_Err, _OtherErr>) // strengthened
      : __base(unexpect, ::cuda::std::move(__unex.error()))
  {}

  _CCCL_API constexpr explicit expected(in_place_t) noexcept
      : __base(true)
  {}

  _CCCL_TEMPLATE(class... _Args)
  _CCCL_REQUIRES(is_constructible_v<_Err, _Args...>)
  _CCCL_API constexpr explicit expected(unexpect_t, _Args&&... __args) noexcept(
    is_nothrow_constructible_v<_Err, _Args...>) // strengthened
      : __base(unexpect, ::cuda::std::forward<_Args>(__args)...)
  {}

  _CCCL_TEMPLATE(class _Up, class... _Args)
  _CCCL_REQUIRES(is_constructible_v<_Err, initializer_list<_Up>&, _Args...>)
  _CCCL_API constexpr explicit expected(unexpect_t, initializer_list<_Up> __il, _Args&&... __args) noexcept(
    is_nothrow_constructible_v<_Err, initializer_list<_Up>, _Args...>) // strengthened
      : __base(unexpect, __il, ::cuda::std::forward<_Args>(__args)...)
  {}

private:
  template <class _Fun, class... _Args>
  _CCCL_API constexpr expected(
    __expected_construct_from_invoke_tag,
    unexpect_t,
    _Fun&& __fun,
    _Args&&... __args) noexcept(is_nothrow_constructible_v<_Err, invoke_result_t<_Fun, _Args...>>)
      : __base(__expected_construct_from_invoke_tag{},
               unexpect,
               ::cuda::std::forward<_Fun>(__fun),
               ::cuda::std::forward<_Args>(__args)...)
  {}

public:
  // [expected.void.dtor], destructor
  // [expected.void.assign], assignment
  _CCCL_EXEC_CHECK_DISABLE
  _CCCL_TEMPLATE(class _OtherErr)
  _CCCL_REQUIRES(is_constructible_v<_Err, const _OtherErr&> _CCCL_AND is_assignable_v<_Err&, const _OtherErr&>)
  _CCCL_API inline _CCCL_CONSTEXPR_CXX20 expected& operator=(const unexpected<_OtherErr>& __un) noexcept(
    is_nothrow_assignable_v<_Err&, const _OtherErr&>
    && is_nothrow_constructible_v<_Err, const _OtherErr&>) // strengthened
  {
    if (this->__has_val_)
    {
      ::cuda::std::__construct_at(::cuda::std::addressof(this->__union_.__unex_), __un.error());
      this->__has_val_ = false;
    }
    else
    {
      this->__union_.__unex_ = __un.error();
    }
    return *this;
  }

  _CCCL_EXEC_CHECK_DISABLE
  _CCCL_TEMPLATE(class _OtherErr)
  _CCCL_REQUIRES(is_constructible_v<_Err, _OtherErr> _CCCL_AND is_assignable_v<_Err&, _OtherErr>)
  _CCCL_API inline _CCCL_CONSTEXPR_CXX20 expected& operator=(unexpected<_OtherErr>&& __un) noexcept(
    is_nothrow_assignable_v<_Err&, _OtherErr> && is_nothrow_constructible_v<_Err, _OtherErr>)
  {
    if (this->__has_val_)
    {
      ::cuda::std::__construct_at(::cuda::std::addressof(this->__union_.__unex_), ::cuda::std::move(__un.error()));
      this->__has_val_ = false;
    }
    else
    {
      this->__union_.__unex_ = ::cuda::std::move(__un.error());
    }
    return *this;
  }

  _CCCL_API constexpr void emplace() noexcept
  {
    if (!this->__has_val_)
    {
      this->__union_.__unex_.~_Err();
      this->__has_val_ = true;
    }
  }

  // [expected.void.swap], swap
  _CCCL_TEMPLATE(class _Err2 = _Err)
  _CCCL_REQUIRES(__expected::__can_swap<void, _Err2>)
  _CCCL_API inline _CCCL_CONSTEXPR_CXX20 void
  swap(expected<void, _Err2>& __rhs) noexcept(is_nothrow_move_constructible_v<_Err2> && is_nothrow_swappable_v<_Err2>)
  {
    if (this->__has_val_)
    {
      if (!__rhs.__has_val_)
      {
        this->__swap_val_unex_impl(*this, __rhs);
      }
    }
    else
    {
      if (__rhs.__has_val_)
      {
        this->__swap_val_unex_impl(__rhs, *this);
      }
      else
      {
        using ::cuda::std::swap;
        swap(this->__union_.__unex_, __rhs.__union_.__unex_);
      }
    }
  }

  template <class _Err2 = _Err>
  friend _CCCL_API inline _CCCL_CONSTEXPR_CXX20 auto
  swap(expected& __x, expected& __y) noexcept(is_nothrow_move_constructible_v<_Err2> && is_nothrow_swappable_v<_Err2>)
    _CCCL_TRAILING_REQUIRES(void)(__expected::__can_swap<void, _Err2>)
  {
    return __x.swap(__y); // some compiler warn about non void function without return
  }

  // [expected.void.obs], observers
  _CCCL_API constexpr explicit operator bool() const noexcept
  {
    return this->__has_val_;
  }

  _CCCL_API constexpr bool has_value() const noexcept
  {
    return this->__has_val_;
  }

  _CCCL_API constexpr void operator*() const noexcept
  {
    _CCCL_ASSERT(this->__has_val_, "expected::operator* requires the expected to contain a value");
  }

  _CCCL_API constexpr void value() const&
  {
    static_assert(is_copy_constructible_v<_Err>, "expected::value() const& requires is_copy_constructible_v<E>");
    if (!this->__has_val_)
    {
      __throw_bad_expected_access<_Err>(this->__union_.__unex_);
    }
  }

  _CCCL_API constexpr void value() &&
  {
    static_assert(is_copy_constructible_v<_Err>, "expected::value() && requires is_copy_constructible_v<E>");
    static_assert(is_move_constructible_v<_Err>, "expected::value() && requires is_move_constructible_v<E>");
    if (!this->__has_val_)
    {
      __throw_bad_expected_access<_Err>(::cuda::std::move(this->__union_.__unex_));
    }
  }

  _CCCL_API constexpr const _Err& error() const& noexcept
  {
    _CCCL_ASSERT(!this->__has_val_, "expected::error requires the expected to contain an error");
    return this->__union_.__unex_;
  }

  _CCCL_API constexpr _Err& error() & noexcept
  {
    _CCCL_ASSERT(!this->__has_val_, "expected::error requires the expected to contain an error");
    return this->__union_.__unex_;
  }

  _CCCL_API constexpr const _Err&& error() const&& noexcept
  {
    _CCCL_ASSERT(!this->__has_val_, "expected::error requires the expected to contain an error");
    return ::cuda::std::move(this->__union_.__unex_);
  }

  _CCCL_API constexpr _Err&& error() && noexcept
  {
    _CCCL_ASSERT(!this->__has_val_, "expected::error requires the expected to contain an error");
    return ::cuda::std::move(this->__union_.__unex_);
  }

  // [expected.void.monadic]
  _CCCL_TEMPLATE(class _Fun, class _Err2 = _Err)
  _CCCL_REQUIRES(is_constructible_v<_Err2, _Err2&>)
  _CCCL_API constexpr auto and_then(_Fun&& __fun) &
  {
    using _Res = remove_cvref_t<invoke_result_t<_Fun>>;

    static_assert(__expected::__is_expected<_Res>, "Result of f(value()) must be a specialization of std::expected");
    static_assert(is_same_v<typename _Res::error_type, _Err>,
                  "The error type of the result of f(value()) must be the same as that of std::expected");

    if (this->__has_val_)
    {
      return ::cuda::std::invoke(::cuda::std::forward<_Fun>(__fun));
    }
    else
    {
      return _Res{unexpect, this->__union_.__unex_};
    }
  }

  _CCCL_TEMPLATE(class _Fun, class _Err2 = _Err)
  _CCCL_REQUIRES(is_copy_constructible_v<_Err2>)
  _CCCL_API constexpr auto and_then(_Fun&& __fun) const&
  {
    using _Res = remove_cvref_t<invoke_result_t<_Fun>>;

    static_assert(__expected::__is_expected<_Res>, "Result of f(value()) must be a specialization of std::expected");
    static_assert(is_same_v<typename _Res::error_type, _Err>,
                  "The error type of the result of f(value()) must be the same as that of std::expected");

    if (this->__has_val_)
    {
      return ::cuda::std::invoke(::cuda::std::forward<_Fun>(__fun));
    }
    else
    {
      return _Res{unexpect, this->__union_.__unex_};
    }
  }

  _CCCL_TEMPLATE(class _Fun, class _Err2 = _Err)
  _CCCL_REQUIRES(is_move_constructible_v<_Err2>)
  _CCCL_API constexpr auto and_then(_Fun&& __fun) &&
  {
    using _Res = remove_cvref_t<invoke_result_t<_Fun>>;

    static_assert(__expected::__is_expected<_Res>, "Result of f(value()) must be a specialization of std::expected");
    static_assert(is_same_v<typename _Res::error_type, _Err>,
                  "The error type of the result of f(value()) must be the same as that of std::expected");

    if (this->__has_val_)
    {
      return ::cuda::std::invoke(::cuda::std::forward<_Fun>(__fun));
    }
    else
    {
      return _Res{unexpect, ::cuda::std::move(this->__union_.__unex_)};
    }
  }

  _CCCL_TEMPLATE(class _Fun, class _Err2 = _Err)
  _CCCL_REQUIRES(is_constructible_v<_Err2, const _Err2>)
  _CCCL_API constexpr auto and_then(_Fun&& __fun) const&&
  {
    using _Res = remove_cvref_t<invoke_result_t<_Fun>>;

    static_assert(__expected::__is_expected<_Res>, "Result of f(value()) must be a specialization of std::expected");
    static_assert(is_same_v<typename _Res::error_type, _Err>,
                  "The error type of the result of f(value()) must be the same as that of std::expected");

    if (this->__has_val_)
    {
      return ::cuda::std::invoke(::cuda::std::forward<_Fun>(__fun));
    }
    else
    {
      return _Res{unexpect, ::cuda::std::move(this->__union_.__unex_)};
    }
  }

  template <class _Fun>
  _CCCL_API constexpr auto or_else(_Fun&& __fun) &
  {
    using _Res = remove_cvref_t<invoke_result_t<_Fun, _Err&>>;

    static_assert(__expected::__is_expected<_Res>,
                  "Result of std::expected::or_else must be a specialization of std::expected");
    static_assert(is_same_v<typename _Res::value_type, void>,
                  "The value type of the result of std::expected::or_else must be the same as that of std::expected");

    if (this->__has_val_)
    {
      return _Res{};
    }
    else
    {
      return ::cuda::std::invoke(::cuda::std::forward<_Fun>(__fun), this->__union_.__unex_);
    }
  }

  template <class _Fun>
  _CCCL_API constexpr auto or_else(_Fun&& __fun) const&
  {
    using _Res = remove_cvref_t<invoke_result_t<_Fun, const _Err&>>;

    static_assert(__expected::__is_expected<_Res>,
                  "Result of std::expected::or_else must be a specialization of std::expected");
    static_assert(is_same_v<typename _Res::value_type, void>,
                  "The value type of the result of std::expected::or_else must be the same as that of std::expected");

    if (this->__has_val_)
    {
      return _Res{};
    }
    else
    {
      return ::cuda::std::invoke(::cuda::std::forward<_Fun>(__fun), this->__union_.__unex_);
    }
  }

  template <class _Fun>
  _CCCL_API constexpr auto or_else(_Fun&& __fun) &&
  {
    using _Res = remove_cvref_t<invoke_result_t<_Fun, _Err>>;

    static_assert(__expected::__is_expected<_Res>,
                  "Result of std::expected::or_else must be a specialization of std::expected");
    static_assert(is_same_v<typename _Res::value_type, void>,
                  "The value type of the result of std::expected::or_else must be the same as that of std::expected");

    if (this->__has_val_)
    {
      return _Res{};
    }
    else
    {
      return ::cuda::std::invoke(::cuda::std::forward<_Fun>(__fun), ::cuda::std::move(this->__union_.__unex_));
    }
  }

  template <class _Fun>
  _CCCL_API constexpr auto or_else(_Fun&& __fun) const&&
  {
    using _Res = remove_cvref_t<invoke_result_t<_Fun, const _Err>>;

    static_assert(__expected::__is_expected<_Res>,
                  "Result of std::expected::or_else must be a specialization of std::expected");
    static_assert(is_same_v<typename _Res::value_type, void>,
                  "The value type of the result of std::expected::or_else must be the same as that of std::expected");

    if (this->__has_val_)
    {
      return _Res{};
    }
    else
    {
      return ::cuda::std::invoke(::cuda::std::forward<_Fun>(__fun), ::cuda::std::move(this->__union_.__unex_));
    }
  }

  _CCCL_TEMPLATE(class _Fun, class _Err2 = _Err)
  _CCCL_REQUIRES(is_constructible_v<_Err2, _Err2&> _CCCL_AND is_same_v<remove_cv_t<invoke_result_t<_Fun>>, void>)
  _CCCL_API constexpr auto transform(_Fun&& __fun) &
  {
    static_assert(invocable<_Fun>, "std::expected::transform requires that F must be invocable with T.");
    if (this->__has_val_)
    {
      ::cuda::std::invoke(::cuda::std::forward<_Fun>(__fun));
      return expected<void, _Err>{};
    }
    else
    {
      return expected<void, _Err>{unexpect, this->__union_.__unex_};
    }
  }

  _CCCL_TEMPLATE(class _Fun, class _Err2 = _Err)
  _CCCL_REQUIRES(is_constructible_v<_Err2, _Err2&> _CCCL_AND(!is_same_v<remove_cv_t<invoke_result_t<_Fun>>, void>))
  _CCCL_API constexpr auto transform(_Fun&& __fun) &
  {
    static_assert(invocable<_Fun>, "std::expected::transform requires that F must be invocable with T.");
    using _Res = remove_cv_t<invoke_result_t<_Fun>>;

    static_assert(__invoke_constructible<_Fun>,
                  "std::expected::transform requires that the return type of F is constructible with the result of "
                  "invoking F");
    static_assert(__expected::__valid_expected<_Res, _Err>,
                  "std::expected::transform requires that the return type of F must be a valid argument for "
                  "std::expected");

    if (this->__has_val_)
    {
      return expected<_Res, _Err>{__expected_construct_from_invoke_tag{}, in_place, ::cuda::std::forward<_Fun>(__fun)};
    }
    else
    {
      return expected<_Res, _Err>{unexpect, this->__union_.__unex_};
    }
  }

  _CCCL_TEMPLATE(class _Fun, class _Err2 = _Err)
  _CCCL_REQUIRES(is_copy_constructible_v<_Err2> _CCCL_AND is_same_v<remove_cv_t<invoke_result_t<_Fun>>, void>)
  _CCCL_API constexpr auto transform(_Fun&& __fun) const&
  {
    static_assert(invocable<_Fun>, "std::expected::transform requires that F must be invocable with T.");
    if (this->__has_val_)
    {
      ::cuda::std::invoke(::cuda::std::forward<_Fun>(__fun));
      return expected<void, _Err>{};
    }
    else
    {
      return expected<void, _Err>{unexpect, this->__union_.__unex_};
    }
  }

  _CCCL_TEMPLATE(class _Fun, class _Err2 = _Err)
  _CCCL_REQUIRES(is_copy_constructible_v<_Err2> _CCCL_AND(!is_same_v<remove_cv_t<invoke_result_t<_Fun>>, void>))
  _CCCL_API constexpr auto transform(_Fun&& __fun) const&
  {
    static_assert(invocable<_Fun>, "std::expected::transform requires that F must be invocable with T");
    using _Res = remove_cv_t<invoke_result_t<_Fun>>;

    static_assert(__invoke_constructible<_Fun>,
                  "std::expected::transform requires that the return type of F is constructible with the result of "
                  "invoking F");
    static_assert(__expected::__valid_expected<_Res, _Err>,
                  "std::expected::transform requires that the return type of F must be a valid argument for "
                  "std::expected");

    if (this->__has_val_)
    {
      return expected<_Res, _Err>{__expected_construct_from_invoke_tag{}, in_place, ::cuda::std::forward<_Fun>(__fun)};
    }
    else
    {
      return expected<_Res, _Err>{unexpect, this->__union_.__unex_};
    }
  }

  _CCCL_TEMPLATE(class _Fun, class _Err2 = _Err)
  _CCCL_REQUIRES(is_move_constructible_v<_Err2> _CCCL_AND is_same_v<remove_cv_t<invoke_result_t<_Fun>>, void>)
  _CCCL_API constexpr auto transform(_Fun&& __fun) &&
  {
    static_assert(invocable<_Fun>, "std::expected::transform requires that F must be invocable with T.");
    if (this->__has_val_)
    {
      ::cuda::std::invoke(::cuda::std::forward<_Fun>(__fun));
      return expected<void, _Err>{};
    }
    else
    {
      return expected<void, _Err>{unexpect, ::cuda::std::move(this->__union_.__unex_)};
    }
  }
  _CCCL_TEMPLATE(class _Fun, class _Err2 = _Err)
  _CCCL_REQUIRES(is_move_constructible_v<_Err2> _CCCL_AND(!is_same_v<remove_cv_t<invoke_result_t<_Fun>>, void>))
  _CCCL_API constexpr auto transform(_Fun&& __fun) &&
  {
    static_assert(invocable<_Fun>, "std::expected::transform requires that F must be invocable with T");
    using _Res = remove_cv_t<invoke_result_t<_Fun>>;

    static_assert(__invoke_constructible<_Fun>,
                  "std::expected::transform requires that the return type of F is constructible with the result of "
                  "invoking F");
    static_assert(__expected::__valid_expected<_Res, _Err>,
                  "std::expected::transform requires that the return type of F must be a valid argument for "
                  "std::expected");

    if (this->__has_val_)
    {
      return expected<_Res, _Err>{__expected_construct_from_invoke_tag{}, in_place, ::cuda::std::forward<_Fun>(__fun)};
    }
    else
    {
      return expected<_Res, _Err>{unexpect, ::cuda::std::move(this->__union_.__unex_)};
    }
  }

  _CCCL_TEMPLATE(class _Fun, class _Err2 = _Err)
  _CCCL_REQUIRES(is_constructible_v<_Err2, const _Err2> _CCCL_AND is_same_v<remove_cv_t<invoke_result_t<_Fun>>, void>)
  _CCCL_API constexpr auto transform(_Fun&& __fun) const&&
  {
    static_assert(invocable<_Fun>, "std::expected::transform requires that F must be invocable with T.");
    if (this->__has_val_)
    {
      ::cuda::std::invoke(::cuda::std::forward<_Fun>(__fun));
      return expected<void, _Err>{};
    }
    else
    {
      return expected<void, _Err>{unexpect, ::cuda::std::move(this->__union_.__unex_)};
    }
  }

  _CCCL_TEMPLATE(class _Fun, class _Err2 = _Err)
  _CCCL_REQUIRES(is_constructible_v<_Err2, const _Err2> _CCCL_AND(!is_same_v<remove_cv_t<invoke_result_t<_Fun>>, void>))
  _CCCL_API constexpr auto transform(_Fun&& __fun) const&&
  {
    static_assert(invocable<_Fun>, "std::expected::transform requires that F must be invocable with T");
    using _Res = remove_cv_t<invoke_result_t<_Fun>>;

    static_assert(__invoke_constructible<_Fun>,
                  "std::expected::transform requires that the return type of F is constructible with the result of "
                  "invoking F");
    static_assert(__expected::__valid_expected<_Res, _Err>,
                  "std::expected::transform requires that the return type of F must be a valid argument for "
                  "std::expected");

    if (this->__has_val_)
    {
      return expected<_Res, _Err>{__expected_construct_from_invoke_tag{}, in_place, ::cuda::std::forward<_Fun>(__fun)};
    }
    else
    {
      return expected<_Res, _Err>{unexpect, ::cuda::std::move(this->__union_.__unex_)};
    }
  }

  template <class _Fun>
  _CCCL_API constexpr auto transform_error(_Fun&& __fun) &
  {
    static_assert(invocable<_Fun, _Err&>, "std::expected::transform_error requires that F must be invocable with E");
    using _Res = remove_cv_t<invoke_result_t<_Fun, _Err&>>;

    static_assert(__invoke_constructible<_Fun, _Err&>,
                  "std::expected::transform_error requires that the return type of F is constructible with the result "
                  "of invoking F");
    static_assert(__expected::__valid_expected<void, _Res>,
                  "std::expected::transform_error requires that the return type of F must be a valid argument for "
                  "std::expected");

    if (this->__has_val_)
    {
      return expected<void, _Res>{};
    }
    else
    {
      return expected<void, _Res>{
        __expected_construct_from_invoke_tag{}, unexpect, ::cuda::std::forward<_Fun>(__fun), this->__union_.__unex_};
    }
  }

  template <class _Fun>
  _CCCL_API constexpr auto transform_error(_Fun&& __fun) const&
  {
    static_assert(invocable<_Fun, const _Err&>,
                  "std::expected::transform_error requires that F must be invocable with E");
    using _Res = remove_cv_t<invoke_result_t<_Fun, const _Err&>>;

    static_assert(__invoke_constructible<_Fun, const _Err&>,
                  "std::expected::transform_error requires that the return type of F is constructible with the result "
                  "of invoking F");
    static_assert(__expected::__valid_expected<void, _Res>,
                  "std::expected::transform_error requires that the return type of F must be a valid argument for "
                  "std::expected");

    if (this->__has_val_)
    {
      return expected<void, _Res>{};
    }
    else
    {
      return expected<void, _Res>{
        __expected_construct_from_invoke_tag{}, unexpect, ::cuda::std::forward<_Fun>(__fun), this->__union_.__unex_};
    }
  }

  template <class _Fun>
  _CCCL_API constexpr auto transform_error(_Fun&& __fun) &&
  {
    static_assert(invocable<_Fun, _Err>, "std::expected::transform_error requires that F must be invocable with E");
    using _Res = remove_cv_t<invoke_result_t<_Fun, _Err>>;

    static_assert(__invoke_constructible<_Fun, _Err>,
                  "std::expected::transform_error requires that the return type of F is constructible with the result "
                  "of invoking F");
    static_assert(__expected::__valid_expected<void, _Res>,
                  "std::expected::transform_error requires that the return type of F must be a valid argument for "
                  "std::expected");

    if (this->__has_val_)
    {
      return expected<void, _Res>{};
    }
    else
    {
      return expected<void, _Res>{
        __expected_construct_from_invoke_tag{},
        unexpect,
        ::cuda::std::forward<_Fun>(__fun),
        ::cuda::std::move(this->__union_.__unex_)};
    }
  }

  template <class _Fun>
  _CCCL_API constexpr auto transform_error(_Fun&& __fun) const&&
  {
    static_assert(invocable<_Fun, const _Err>,
                  "std::expected::transform_error requires that F must be invocable with E");
    using _Res = remove_cv_t<invoke_result_t<_Fun, const _Err>>;

    static_assert(__invoke_constructible<_Fun, const _Err>,
                  "std::expected::transform_error requires that the return type of F is constructible with the result "
                  "of invoking F");
    static_assert(__expected::__valid_expected<void, _Res>,
                  "std::expected::transform_error requires that the return type of F must be a valid argument for "
                  "std::expected");

    if (this->__has_val_)
    {
      return expected<void, _Res>{};
    }
    else
    {
      return expected<void, _Res>{
        __expected_construct_from_invoke_tag{},
        unexpect,
        ::cuda::std::forward<_Fun>(__fun),
        ::cuda::std::move(this->__union_.__unex_)};
    }
  }

  // [expected.void.eq], equality operators
  _CCCL_EXEC_CHECK_DISABLE
  friend _CCCL_API constexpr bool operator==(const expected& __x, const expected& __y) noexcept
  {
    if (__x.__has_val_ != __y.has_value())
    {
      return false;
    }
    else
    {
      return __x.__has_val_ || static_cast<bool>(__x.__union_.__unex_ == __y.error());
    }
  }
#if _CCCL_STD_VER < 2020
  _CCCL_EXEC_CHECK_DISABLE
  friend _CCCL_API constexpr bool operator!=(const expected& __x, const expected& __y) noexcept
  {
    return !(__x == __y);
  }
#endif // _CCCL_STD_VER < 2020

  _CCCL_EXEC_CHECK_DISABLE
  template <class _E2>
  friend _CCCL_API constexpr bool operator==(const expected& __x, const expected<void, _E2>& __y) noexcept
  {
    if (__x.__has_val_ != __y.has_value())
    {
      return false;
    }
    else
    {
      return __x.__has_val_ || static_cast<bool>(__x.__union_.__unex_ == __y.error());
    }
  }
#if _CCCL_STD_VER < 2020
  _CCCL_EXEC_CHECK_DISABLE
  template <class _E2>
  friend _CCCL_API constexpr bool operator!=(const expected& __x, const expected<void, _E2>& __y) noexcept
  {
    return !(__x == __y);
  }
#endif // _CCCL_STD_VER < 2020

  _CCCL_EXEC_CHECK_DISABLE
  template <class _E2>
  friend _CCCL_API constexpr bool operator==(const expected& __x, const unexpected<_E2>& __y) noexcept
  {
    return !__x.__has_val_ && static_cast<bool>(__x.__union_.__unex_ == __y.error());
  }
#if _CCCL_STD_VER < 2020
  _CCCL_EXEC_CHECK_DISABLE
  template <class _E2>
  friend _CCCL_API constexpr bool operator==(const unexpected<_E2>& __y, const expected& __x) noexcept
  {
    return !__x.__has_val_ && static_cast<bool>(__x.__union_.__unex_ == __y.error());
  }
  _CCCL_EXEC_CHECK_DISABLE
  template <class _E2>
  _CCCL_API friend constexpr bool operator!=(const expected& __x, const unexpected<_E2>& __y) noexcept
  {
    return __x.__has_val_ || static_cast<bool>(__x.__union_.__unex_ != __y.error());
  }
  _CCCL_EXEC_CHECK_DISABLE
  template <class _E2>
  _CCCL_API friend constexpr bool operator!=(const unexpected<_E2>& __y, const expected& __x) noexcept
  {
    return __x.__has_val_ || static_cast<bool>(__x.__union_.__unex_ != __y.error());
  }
#endif // _CCCL_STD_VER < 2020
};

_CCCL_END_NAMESPACE_CUDA_STD

#include <cuda/std/__cccl/epilogue.h>

#endif // _CUDA_STD___EXPECTED_EXPECTED_H
